Data terminal equipment (DTE) devices include any device that can be connected to a network, ranging from computers, servers and laptops, through home appliances such as televisions, video recorders and stereos, to Internet Protocol (IP) phones and facsimile machines. Some DTE devices receive electrical power from an internal source such as a power supply or plug-type power adapter or receive electrical power from an external power source. Other devices require their electrical power to be supplied directly through the network cables. Such devices are referred to as Powered Devices (PD), while devices with power supplying capabilities are referred to as Power Sourcing Equipment (PSE) devices. When a PSE and a PD are interconnected, the PD draws its electrical power from the PSE.
In order to maintain interoperability, a PSE must not cause a malfunction when it is connected to a non powered device. A requirement of the PSE, therefore, is that it must have a method of detecting powered devices. Further, the method must be sufficiently secure so that the PSE will not source power to a non powered device. In addition, a PSE must not be fooled into sourcing power by another PSE.
A block diagram illustrating a prior art common example of an Ethernet network topology comprising IP phones, personal computers (PCs) and laptops is shown in FIG. 1. The example network, generally referenced 10, comprises IP phone 12, laptop 14 and IP phone 16, all connected to an Ethernet switch 20. Personal computer (PC) 18 is connected to the network through IP phone 16. In operation, the Ethernet switch controls the network traffic and is also responsible for sourcing power only to devices that require it, such as the IP phones.
Thus, there is a need for a mechanism for detecting the presence of power requiring devices over a communications network. The mechanism must not fool other devices so that the PSE sources power to non powered devices and it must not be fooled into sourcing power by another PSE.